Systems and Methods of Handing Over a Wireless Device

ABSTRACT

A source base station determines that a wireless device is to be handed over from the source base station to a target base station and sends, to the target base station in a handover signaling message, a current mapping between two or more flow identifiers and a first data radio bearer used for communication between the wireless device and the source base station. The source base station receives, from the target base station, an indication that the current mapping is to be used and hands over the wireless device from the source base station to the target base station.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/535,452, which was filed on Jun. 13, 2017, which is anational stage application of PCT/EP2017/058241, which was filed Apr. 6,2017, and claims benefit of U.S. Provisional Application 62/417,984,which was filed Nov. 4, 2016, the entire disclosure of each of which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates generally to the field of communications,and in particular to handing over a wireless device from a source basestation to a target base station.

BACKGROUND

The standardization organization 3GPP is currently in the processes ofspecifying a new Radio Interface called NR or 5G or G-UTRA as well as aNext Generation Packet Core Network (NGCN or NGC). The Next Gen RadioAccess Network (RAN) may contain base stations support evolved LTEand/or NR radio access. There has been some agreement on a Quality ofService (QoS) concept for Next Gen System. Aspects of this QoS conceptinclude that the RAN is provided with packet marking over the user planebetween RAN and Core Network. The marking may include a flow identifier(ID) which the RAN later uses to provide QoS treatment over the radio.It may be up to RAN to define the AS-level QoS of Data Radio Bearers(DRBs) and how uplink and downlink packets are mapped to DRBs.

One of the problems with existing solutions is that after a wirelessdevice has been handed over from a source base station to a target basestation a reduction of end user and system performance could beapplicable because different base stations may have different ways to domapping of Flow IDs to Data Radio Bearers.

SUMMARY

It is an object of the present invention to improve the QoS handling ina hand-over scenario of a wireless device between base stations.

This object is achieved by the independent claims. Advantageousembodiments are described in the dependent claims.

According to an aspect, a method performed by a source base station ofhanding over a wireless device from the source base station to a targetbase station is provided. Said method comprises determining that awireless device is to be handed over from the source base station to thetarget base station; and sending, to the target base station, a currentmapping between one or more flow identifiers and a first set of dataradio bearers used for communication between the wireless device and thesource base station.

According to a further aspect, a source base station for handing over awireless device to a target base station is provided. The source basestation the source base station comprising a processor and a memory,said memory containing instructions executable by said processor,whereby said source base station is operative to determine that thewireless device is to be handed over from the source base station to thetarget base station. The source base station is further operative tosend, to the target base station, a current mapping between one or moreflow identifiers and a first set of data radio bearers used forcommunication between the wireless device and the source base station.

According to a further aspect, a source base station for handing over awireless device to a target base station is provided. The source basestation comprises a processing circuit configured to determine that thewireless device is to be handed over from the source base station to thetarget base station. The processing circuit is further configured tosend, to the target base station, a current mapping between one or moreflow identifiers and a first set of data radio bearers used forcommunication between the wireless device and the source base station.

According to a further aspect, a method performed by a wireless deviceof handing over the wireless device from a source base station to atarget base station if provided. Said method comprises determining thatthe wireless device is to be handed over from the source base station tothe target base station; and sending, to the target base station, acurrent mapping between one or more flow identifiers and a first set ofdata radio bearers used for communication between the wireless deviceand the source base station.

According to a further aspect, a wireless device that is capable ofbeing handed over from a source base station to a target base station isprovided. Said wireless device comprising a processor and a memory, saidmemory containing instructions executable by said processor, wherebysaid wireless device is operative to determine that the wireless deviceis to be handed over from the source base station to the target basestation. The wireless device is further operative to send, to the targetbase station, a current mapping between one or more flow identifiersassociated with respective packet flows originating or terminating atthe wireless device and a first set of data radio bearers used forcommunication between the wireless device and the source base station.

According to a further aspect, a wireless device that is capable ofbeing handed over from a source base station to a target base station isprovided. Said wireless device comprises a processing circuit configuredto determine that the wireless device is to be handed over from thesource base station to the target base station. The processing circuitis further configured to send, to the target base station, a currentmapping between one or more flow identifiers associated with respectivepacket flows originating or terminating at the wireless device and afirst set of data radio bearers used for communication between thewireless device and the source base station

According to a further aspect, a method performed by the target basestation of handing over a wireless device from a source base station tothe target base station is provided. Said method comprises obtaining acurrent mapping between one or more flow identifiers and a first set ofdata radio bearers used for communication between the wireless deviceand the source base station and determining a new mapping between theone or more flow identifiers and a second set of data radio bearers usedfor communication between the wireless device and the target basestation. The method further comprises signaling the new mapping to thewireless device.

According to a further aspect, a target base station for handing over awireless device from a source base station to the target base station isprovided. Said target base station comprising a processor and a memory,said memory containing instructions executable by said processor,whereby said target base station is operative to obtain a currentmapping between one or more flow identifiers associated with respectivepacket flows originating or terminating at the wireless device and afirst set of data radio bearers used for communication between thewireless device and the source base station. The target base station isfurther operative to determine a new mapping between the one or moreflow identifiers and a second set of data radio bearers used forcommunication between the wireless device and the target base station,and signal, to the wireless device, the new mapping

According to a further aspect, a target base station for handing over awireless device from a source base station to the target base station isprovided. Said target base station comprises a processing circuitconfigured to obtain a current mapping between one or more flowidentifiers associated with respective packet flows originating orterminating at the wireless device and a first set of data radio bearersused for communication between the wireless device and the source basestation. The processing circuit is further configured to determine a newmapping between the one or more flow identifiers and a second set ofdata radio bearers used for communication between the wireless deviceand the target base station, and signal, to the wireless device, the newmapping.

One advantage of the above mentioned aspects is to enable the flow toDRB mapping also after a handover from a source to a target basestation, which means that QoS differentiation according to operatorpolicies may be applied also in the target base station which leads toimproved end user and system performance.

One further advantage is that the flow to DRB mapping appliesimmediately when the UE arrives in the target base station or cell whichreduces delay.

BRIEF DESCRIPTION OF THE FIGURES

The present disclosure will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of thedisclosure are shown. However, this disclosure should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. Like numbers refer to like elements throughout.

FIG. 1 illustrates one embodiment of a system for handing over awireless device in accordance with various aspects as described herein.

FIG. 2 illustrates one embodiment of a system for QoS mapping andfiltering in accordance with various aspects as described herein.

FIG. 3 illustrates one embodiment of a system for mapping packets toflows in accordance with various aspects as described herein.

FIG. 4 illustrates one embodiment of a method of handover implemented bythe source base station in accordance with various aspects as describedherein.

FIG. 5 illustrates one embodiment of a method of handover implemented bythe wireless device in accordance with various aspects as describedherein.

FIG. 6 illustrates one embodiment of a method of handover implemented bythe target base station in accordance with various aspects as describedherein.

FIG. 7 illustrates one embodiment of a source base station or otherradio network node in accordance with various aspects as describedherein.

FIG. 8 illustrates one embodiment of a target base station or otherradio network node in accordance with various aspects as describedherein.

FIG. 9 illustrates one embodiment of a wireless device in accordancewith various aspects as described herein.

FIG. 10 illustrates another embodiment of a wireless device inaccordance with various aspects as described herein.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the present disclosure isdescribed by referring mainly to an exemplary embodiment thereof. In thefollowing description, numerous specific details are set forth in orderto provide a thorough understanding of the present disclosure. However,it will be readily apparent to one of ordinary skill in the art that thepresent disclosure may be practiced without limitation to these specificdetails. In this description, well known methods and structures have notbeen described in detail so as not to unnecessarily obscure the presentdisclosure.

This disclosure includes describing systems and methods for sharingchannel information between co-located radio nodes. For instance, FIG. 1illustrates one embodiment of a system 10 for handing over a wirelessdevice 300 in accordance with various aspects as described herein. Thewireless device or UE 300 is connected to a base station 100, denoted assource base station 100 via a connection 43. The source base station 100is adapted to provide connection in a cell 35. The wireless device/UE300 or the network may determine that the wireless device/UE 300 isbetter served by the other base station 200 which also serves a cell 35,which can be named as a target base station 200. The source base station100 and the target base station 200 may be connected via a X2-interfaceor XN-interface 41. Base stations 100, 200 may be part of a NextGen RAN30 supporting evolved LTE and/or New Radio (NR) radio access.

Both, the source base station 100 and the target base station 200 areconnected via reference points NG2 (control plane) and NG3 (user plane)to a core network node 25, which may be part of a NextGen Core network20. The NextGen Core network 20 is connected via NG6 reference point toa Data network (PDN) 40. The Data network may be an operator externalpublic or private data network or an intra-operator data network, e.g.for provision of IMS services. This reference point may correspond toSGi for 3GPP accesses. The Data network and the NextGen Core network 20may be part of a core network 10.

FIG. 2 illustrates one embodiment of a system of QoS mapping andfiltering in accordance with various aspects as described herein. Inthis example the wireless device 300, which can be a User Equipment (UE)in this embodiment, comprises Uplink (UL) Packet Filters (TFT) which areadapted to determine, based on the source and destination IP addressesand port numbers, in which bearer to carry each packet. Each TFT isallocated to an Evolved Packet System (EPS) radio bearer between the UE300 and a radio base station 100, 200, which is depicted as a eNodeB(eNB) in the example of FIG. 2 . The radio base stations 100, 200 can beradio base stations according to any standard, like 4G (LTE) or 5G(NR=New Radio). On the core network side between the eNB 100, 200 andthe Packet Date Network (PDN) Gateway (GW) 25, Downlink (DL) PacketFilter (TFT) are installed to map the DL Service Data Flows (SDF) to S1data flows towards the eNB 100, 200.

FIG. 3 illustrates one embodiment of a system of mapping packets toflows in accordance with various aspects as described herein. Thisfigure depicts the changes expected for the next generation (NextGen)core network (CN). Instead of mapping IP packets to EPS bearers as thishas been depicted in FIG. 2 , the NextGen core network is supposed togroup packets into flows. This may be done by packet filters similar tothe TFTs defined in EPS. The NextGen CN and the UE 300 could ensure thatall packets to and from, for example the same IP/Port number tuple,belong to a “flow”. On their way through the transport network eachpacket may be marked with some sort of “Flow ID”. In FIG. 3 thesefilters are denoted as Non-Access Stratum (NAS) filters which maps datapackets to flows. Like in Evolved (E)-UTRA/Evolved Packet Core (EPC),the core network determines and applies the downlink filters locally andit may configure the UE 300 by means of NAS signalling with a set ofuplink “NAS filters” included in one or multiple pre-authorized QoSrules. The QoS rules may have been pre-authorized at the Protocol DataUnit (PDU) session establishment or during the lifetime of the PDUsession.

In the UE 300, Access-Stratum (AS) filters have been introduced whichmaps the flows to the data radio bearers (DRB). The AS is allocated toLayer 1 and 2, wherein NAS is allocated to higher layers (above PDCP/RRClayer). In the example of FIG. 3 the IP packets (in service data flows)are mapped to three different flows which have been marked withhorizontal, vertical and transversal lines. The three flows in thisembodiment are further mapped via the AS filters to two Data RadioBearers which have been marked in black and white. However, it is clearfor a person skilled in the art to have more or less flows which couldbe mapped to more or less data radio bearers. In the radio base station100, 200 which is a eNB in the embodiment, the AS filters map the DataRadio Bearers to Packets with flow IDs or similar indications. The NASfilters are included in the gateway (GW) 25 which then maps the packetswith flow IDs to the IP packets in service data flows. The direction ofthe packet flow can be uplink or downlink direction.

The AS filters determine the DRB by just looking at the “flow ID” of theincoming packet, i.e., the AS layer does not need to be aware ofservices, traffic-flow-templates and address/port tuples. The NASfilters, on the other hand, determine the mapping from services to “flowID” but do not need to be aware of DRBs. The two-step filtering fitswell to the pre-configured QoS mapping (a.k.a. pre-authorized QoS). TheeNB 100, 200 determines for each flow ID the DRB and may provide such aconfiguration to the UE 300 via RRC (Radio Resource Control). This ASconfiguration is independent of the corresponding NAS mapping (IPpackets to “flows”) except that the AS and NAS should use a common setof flow IDs. Hence, the RAN configures the “AS filters” whereas the CNconfigures the “NAS filters”.

Similarly, to the PDN Connections in EPS the NextGen CN will supportmultiple PDU sessions. Each PDU session is mapped to a separatetransport network bearer in order to separate them even if the containedpackets have an overlapping IP address range. Also the UE 300 must beable to determine which IP packet belongs to which PDN session in orderto route packets correctly. This may also need to be taken into accountin the reflective QoS filtering.

It may be noted that in all steps listed below in the differentembodiments, where the information about mapping of flow identifiers todata radio bearers is provided, this mapping information may be enhancedby also providing the mapping of flow identifiers to the PDU Session IDeach flow identifier is associated with. The encoding may be done in aper flow ID manner or by grouping flow identifiers that belong to aparticular PDU Session ID.

In the following embodiments it is assumed that a wireless device or UE300 is connected to a base station, which is referred to as source basestation 100 and that the UE 300 may start sending or receiving data. Itis further assumed that the data may be associated with different flowswhich are identified by their flow IDs. The classification of flows isperformed in the UE 300 in the uplink direction (from UE 300 to sourcebase station 100) and in the core network for downlink direction (fromthe source radio base station 100 to the UE 300).

FIG. 4 illustrates an exemplary method 400 of handover implemented bythe source base station 100. The method 400 is implemented when awireless device 300, served by the source base station 100, is to behanded over to a target base station 200. The method begins with thesource base station 100 determining that a wireless device 300 is to behanded over from the source base station 100 to the target base station200 (block 410). Responsive to the determination, the source basestation 100 sends, to the target base station 200, a current mappingbetween one or more flow identifiers associated with respective packetflows originating or terminating at the wireless device and a first setof data radio bearers used for communication between the wireless deviceand the source base station (block 420). The current mapping may bereceived from a network node or from the wireless device 300.

The source base station may send the current mapping directly to thetarget base station 200 over a side haul interface, or indirectly viaanother network node (e.g., wireless device 300 or core network node).

According to a further embodiment the source base station 100 receives,from the target base station 200, an indication of a new mapping betweenthe one or more flow identifiers and a second set of data radio bearersused for communication between the wireless device 300 and the targetbase station 200. This indication is sent to the wireless device 300. Inanother embodiment the indication of the new mapping between the one ormore flow identifiers and a second set of data radio bearers used forcommunication between the wireless device 300 and the target basestation 200 is received from the wireless device 300 and is sent to thetarget base station 200. The sending of the new mapping could be doneprior to or contemporaneous with or after the wireless device 300 beinghanded over to the target base station 200. These further embodimentsallow to use different number of DRBs in target and source base stationor cell. Changing the flow ID to DRB mapping in the target base station200 enables optimized performance in the target base station 200considering local configuration, load or radio conditions

FIG. 5 illustrates a corresponding method 500 of handover implemented bythe wireless device 300. The method 500 is implemented when the wirelessdevice 300 is to be handed over from a source base station 100 to atarget base station 200. The method begins with the wireless device 300determining that it is to be handed over from the source base station100 to the target base station 200 (block 510). Responsive to thedetermination, the wireless device 300 sends, to the target base station200, a current mapping between one or more flow identifiers associatedwith respective packet flows originating or terminating at the wirelessdevice 300 and a first set of data radio bearers used for communicationbetween the wireless device 300 and the source base station 100 (block520). The wireless device 300 may send the current mapping to the targetbase station 200 prior to executing the handover, during the handover,or immediately after the handover.

According to a further embodiment the sending of the current mapping maybe done via the source base station 100.

According to a further embodiment the current mapping of the flowidentifier to the data radio bearer may be conveyed by the wirelessdevice 300 from the source base station 100 to the target base station200. It may also be possible for the wireless device 300 to receiveinformation from the network, which might be the source or target radiobase station 100, 200, how to perform the flow identifier to data radiobearer mapping in the target base station 200 or cell. This embodimentmay allow the use of a different number of data radio bearers in thetarget and source base station/cell 100.

According to a further embodiment the information transferred to thewireless device 300 may be transferred as part of control plane message(e.g. RRC), or user plane signaling (e.g. PDCP, RLC, MAC). The messagesmay be part of the handover procedure between two base station 100, 200,or state transition procedure (e.g. when wireless device or UE 300returns to active state from some power saving state).

According to a further embodiment a new mapping between the one or moreflow identifiers and a second set of data radio bearers used forcommunication between the wireless device 300 and the target basestation 200 is obtained. Said obtaining may include receiving, from thetarget base station 200, an indication of the new mapping. Saidreceiving may be done via the source base station 100. An indicationthat acknowledges receiving of the new mapping may be sent to the targetbase station 200. Said sending of the acknowledgement indication may bedone via the source base station 100. The acknowledgment may betransferred over a network interface and/or over the radio interface,prior or after the wireless device 300 has arrived in the target basestation 200. The advantage of having the mapping prior the wirelessdevice 300 has arrived at the target base station 200 is that thewireless device 300 can use the new mapping as soon as traffic starts inthe target base station 200 or cell or at a later stage.

According to a further embodiment the new mapping is the same as thecurrent mapping. It may also be possible that the new mapping removes oradds a data radio bearer from/to the first set to obtain the second set.

According to a further embodiment the mapping may be signaled explicitlyto the wireless device 300 or may be conveyed implicitly using thereflective QoS concept where the target base station 200 or RAN nodemaps DL packets to a given data radio bearer, and then the wirelessdevice 300 will perform similar mapping of UL packets associated withthe same application or transport flow to the same data radio bearer inthe UL. In other words, the wireless device 300, after it has beenhanded over to the target base station 200, may receive, from the targetbase station 200, one or more flow identifiers associated with one ormore downlink packet flows on a new data radio bearer used forcommunication between the wireless device 300 and the target basestation 200. The wireless device 300 then maps the one or more flowidentifiers to the one or more uplink packet flows and transmits the oneor more uplink packet flows on the new data radio bearer to the targetbase station 200. This embodiment has the advantage that no explicitsignaling of mapping information between Flow ID and DRB to the wirelessdevice 300 is necessary. The wireless device 300 just reflects the QoSsetting which it has received towards the target base station 200.

According to a further embodiment the wireless device 300, after it hasbeen handed over to the target base station 200, maps the one or moreflow identifiers to a default data radio bearer used for communicationbetween the wireless device 300 and the target base station 200. Thisembodiment has the advantage that the mapping to a default bearer can bedone even if the transfer of mapping information failed or is notpossible.

According to a further embodiment the wireless device 300 maps the oneor more flow identifiers to the first set based on the current mappingafter a failed handover to the target base station 200.

The one or more flow identifiers may be associated with respectivepacket flows originating or terminating at the wireless device 300. Theflow ID may be conveyed together with UL or DL packets. According to afurther embodiment the flow ID may be signaled separately. This allows amore flexible handling of signaling messages so that it is not necessaryto adapt already existing messages.

The source base station 100 may send the current mapping to the targetbase station 200 prior to executing the handover, during the handover orcontemporaneous with the handover, or immediately after the handover.The advantage of providing the mapping prior to the handover is that thetarget base station 200 is already aware of the existing mapping suchthat the target base station 200 can take over the communication veryfast after the handover procedure without much delay. If the mapping isprovided during or contemporaneously with the handover the control datatraffic is reduced because the mapping could be integrated in thehandover signaling. If the mapping is provided immediately after thehandover, the risk of providing mapping information even if the handoveris failed, is very low.

The one or more flow identifiers may be associated with respectivepacket flows originating or terminating at the wireless device.Providing means for efficient signaling of the flow ID to data radiobearer mapping over the radio minimizing overhead, maximized the chanceof delivery of critical message (such as handover command).

The signaling of the current or new data radio bearer to flow mappingmay be performed over an interface between the target and source basestation (e.g. X2, XN) or via other nodes e.g. CN nodes (via S1/NG-2).The mapping may be conveyed in a signaling message. The signalingmessage may be related to handover signaling or context fetch signaling.

FIG. 6 illustrates a method 600 of handover implemented by the targetbase station 200. The method 600 is implemented when the wireless device300 is to be handed over from a source base station 100 to the targetbase station 200. To begin, the target base station 200 obtains acurrent mapping between one or more flow identifiers associated withrespective packet flows originating or terminating at the wirelessdevice 300 and a first set of data radio bearers used for communicationbetween the wireless device 300 and the source base station 100 (block610). The target base station 200 may obtain the current mappingdirectly from the source base station 100, indirectly from the sourcebase station 100 via a network node in the core network 20, or from thewireless device 300 that is being handed over. After receiving thecurrent mapping, the target base station 200 determines a new mappingbetween the one or more flow identifiers and a second set of data radiobearers used for communication between the wireless device 300 and thetarget base station 200 (block 620). The target base station 200 signalsthe new mapping or an indication of the new mapping to the wirelessdevice 300 (block 630). The sending may be done via the source basestation 100.

The target base station 200 may indicate in a further embodiment thatthe current mapping should be used. This indication may either beexplicit (via a signaling flag) or implicit from the fact that thenumber of data radio bearers are the same and no new mapping issignaled. The target base station 200 may indicate that the number ofdata radio bearers should be reduced and that some flows which mapped onone data radio bearer should be moved to another data radio bearer. Thismay either be explicit (e.g. flow 1, 3, 7 should be moved to data radiobearer 4) or there could be some implicit rules in the wireless device300 saying that if a data radio bearer is removed all flows mapped onthat data radio bearer should be mapped on another data radio bearer(e.g. a default data radio bearer, or a data radio bearer of lower orhigher priority). The target base station 200 may indicate that thenumber of data radio bearers should be increased and that some flowsmapped on one data radio bearer should be moved to another data radiobearer. This may either be explicit (e.g. flow 1, 3, 7 should be movedto data radio bearer 4) or there could be some implicit rules in thewireless device 300 saying that if a data radio bearer is added someflows (e.g. associated with a certain QoS) mapped on another data radiobearer should be moved to this data radio bearer.

According to a further embodiment, no flows may initially be mapped tothe new data radio bearer which was added after the mobility event.Instead, the target base station 200 may upon arrival of the wirelessdevice or UE 300 start moving some old or new incoming flows to the newdata radio bearer. The moving of flows may be done explicitly or usingthe reflective QoS concept where the data radio bearer starts mapping DLpackets on the new data radio bearer, and the wireless device 300 mapscorresponding UL packet associated with the same session on the samedata radio bearer in UL.

According to a further embodiment said receiving is prior to orcontemporaneous with or after the wireless device being handed over tothe source base station 100.

According to a further embodiment said determining includes determiningthat the new mapping is the same as the current mapping or determiningthat the new mapping removes or adds a data radio bearer from/to thefirst set to obtain the second set. Said determining may also includethat after the wireless device 300 has been handed over to the targetbase station 200, determining a new mapping between the one or more flowidentifiers and a new data radio bearer of the second set.

According to a further embodiment said determining includes that afterthe wireless device 300 has been handed over to the target base station200, determining a new mapping between the one or more flow identifiersassociated with one or more downlink packet flows on a new data radiobearer used for communication between the wireless device 300 and thetarget base station 200.

According to a further embodiment the target base station 200 transmitsto the wireless device 300 the one or more downlink packet flows on thenew data radio bearer based on the new mapping; and in response to saidtransmitting, receiving, from the wireless device 300, one or moreuplink packet flows on the new data radio bearer that are mapped to theone or more flow identifiers.

According to a further embodiment the one or more flow identifiers areassociated with respective packet flows originating or terminating atthe wireless device 300.

FIG. 7 illustrates an exemplary a source base station 100 or anotherradio network node configured to operate as herein described. Accordingto one embodiment the source base station 100 is for handing over awireless device 300 to a target base station 200. The source basestation 100 is configured to determine that the wireless device 300 isto be handed over from the source base station 100 to the target basestation 200 and to send, to the target base station 200, a currentmapping between one or more flow identifiers and a first set of dataradio bearers used for communication between the wireless device 300 andthe source base station 100. According to a further embodiment the basestation 100 comprises an interface circuit 110, processing circuit 120,and memory 140. The interface circuit 110 is coupled to one or moreantennas 115 and comprises the radio frequency (RF) components neededfor communicating with the wireless devices 300 over a wirelesscommunication channel. Typically, the RF components include atransmitter and receiver adapted for communications according to the NRor 5G standard, or other standard where mapping of flow identifiers todata radio bearers is used.

The processing circuit 120 processes the signals transmitted to orreceived by the base station 100. Such processing includes coding andmodulation of transmitted signals, and the demodulation and decoding ofreceived signals. In one embodiment, the processing circuit 120comprises a determination unit 125 for determining that a wirelessdevice 300 will be handed over to a target base station 200, and asignaling unit 130 for sending a current mapping of flow identifiers toa first set of data radio bearers used for communication between thewireless device 300 and the source base station 100. The processingcircuit 120 may comprise one or more microprocessors, hardware,firmware, or a combination thereof. In one embodiment, the determinationunit 125 and signaling unit 130 are implemented by a singlemicroprocessor. In other embodiments, the determination unit 125 andsignaling unit 130 may be implemented using different microprocessors.

Memory 140 comprises both volatile and non-volatile memory for storingcomputer program code and data needed by the processing circuit 120 foroperation. Memory 140 may comprise any tangible, non-transitorycomputer-readable storage medium for storing data including electronic,magnetic, optical, electromagnetic, or semiconductor data storage.Memory 140 stores a computer program 150 comprising executableinstructions that configure the processing circuit 120 to implementmethods 400 according to FIG. 4 . In general, computer programinstructions and configuration information are stored in a non-volatilememory, such as a read only memory (ROM), erasable programmable readonly memory (EPROM) or flash memory. Temporary data generated duringoperation may be stored in a volatile memory, such as a random accessmemory (RAM). In some embodiments, the computer program 150 forconfiguring the processing circuit 120 as herein described may be storedin a removable memory, such as a portable compact disc, portable digitalvideo disc, or another removable media.

The computer program 150 may also be embodied in a carrier such as anelectronic signal, optical signal, radio signal, or computer readablestorage medium.

FIG. 8 illustrates an exemplary target base station 200 or another radionetwork node configured to operate as herein described. According to oneembodiment the target base station 200 for handing over a wirelessdevice 300 from a source base station 100 to the target base station 200is configured to obtain a current mapping between one or more flowidentifiers associated with respective packet flows originating orterminating at the wireless device 300 and a first set of data radiobearers used for communication between the wireless device 300 and thesource base station 100 and determine a new mapping between the one ormore flow identifiers and a second set of data radio bearers used forcommunication between the wireless device 300 and the target basestation 200; and signal, to the wireless device 300, the new mapping.

The target base station 200 comprises an interface circuit 210,processing circuit 220, and memory 240. The interface circuit 210 iscoupled to one or more antennas 215 and comprises the radio frequency(RF) components needed for communicating with the wireless devices 300over a wireless communication channel. Typically, the RF componentsinclude a transmitter and receiver adapted for communications accordingto the NR or 5G standard, or other standard where mapping of flowidentifiers to data radio bearers is used.

The processing circuit 220 processes the signals transmitted to orreceived by the target base station 200. Such processing includes codingand modulation of transmitted signals, and the demodulation and decodingof received signals. In one embodiment, the processing circuit 220comprises an acquisition unit 225 for obtaining a current mapping offlow identifiers to a first set of data radio bearers used forcommunication between the wireless device 300 and the source basestation 200, a mapping unit 230 for determining a new mapping betweenthe flow identifiers and a second set of data radio bearers used forcommunication between the wireless device 300 and the target basestation 200, and a signaling unit 235 for sending the new mapping to thewireless device 300. The processing circuit 220 may comprise one or moremicroprocessors, hardware, firmware, or a combination thereof. In oneembodiment, the acquisition unit 225, mapping unit 230, and signalingunit 235 are implemented by a single microprocessor. In otherembodiments, the acquisition unit 225, mapping unit 230, and signalingunit 235 may be implemented using different microprocessors.

Memory 240 comprises both volatile and non-volatile memory for storingcomputer program code and data needed by the processing circuit 220 foroperation. Memory 240 may comprise any tangible, non-transitorycomputer-readable storage medium for storing data including electronic,magnetic, optical, electromagnetic, or semiconductor data storage.Memory 240 stores a computer program 250 comprising executableinstructions that configure the processing circuit 220 to implementmethods 400 according to FIG. 6 . In general, computer programinstructions and configuration information are stored in a non-volatilememory, such as a read only memory (ROM), erasable programmable readonly memory (EPROM) or flash memory. Temporary data generated duringoperation may be stored in a volatile memory, such as a random accessmemory (RAM). In some embodiments, the computer program 250 forconfiguring the processing circuit 220 as herein described may be storedin a removable memory, such as a portable compact disc, portable digitalvideo disc, or other removable media. The computer program 250 may alsobe embodied in a carrier such as an electronic signal, optical signal,radio signal, or computer readable storage medium.

FIG. 9 illustrates an exemplary wireless device 300 configured tooperate as herein described. According to one embodiment the wirelessdevice 300 is capable of being handed over from a source base station100 to a target base station 200, said wireless device 300 is configuredto determine that the wireless device 300 is to be handed over from thesource base station 100 to the target base station 200, and to send, tothe target base station 200, a current mapping between one or more flowidentifiers associated with respective packet flows originating orterminating at the wireless device 300 and a first set of data radiobearers used for communication between the wireless device 300 and thesource base station 100.

According to a further embodiment the wireless device 300 comprises aninterface circuit 330, processing circuit 320, and memory 340. Theinterface circuit 330 is coupled to one or more antennas 315 andcomprises the radio frequency (RF) components needed for communicatingwith the base stations 100 and 200 over a wireless communicationchannel. Typically, the RF components include a transmitter and receiveradapted for communications according to the NR or 5G standard, or otherstandard where mapping of flow identifiers to data radio bearers isused.

The processing circuit 320 processes the signals transmitted to orreceived by the wireless device 300. Such processing includes coding andmodulation of transmitted signals, and the demodulation and decoding ofreceived signals. In one embodiment, the processing circuit 320comprises a determination unit 325 for determining that the wirelessdevice 300 will be handed over from a source base station 100 to atarget base station 200 and a signaling unit 330 for sending, to thetarget base station 200, a current mapping of flow identifiers to afirst set of data radio bearers used for communication between thewireless device 300 and the source base station 100. The processingcircuit 320 may comprise one or more microprocessors, hardware,firmware, or a combination thereof. In one embodiment, the determinationunit 325 and signaling unit 330 are implemented by a singlemicroprocessor. In other embodiments, the determination unit 325 andsignaling unit 330 may be implemented using different microprocessors.

Memory 340 comprises both volatile and non-volatile memory for storingcomputer program code and data needed by the processing circuit 320 foroperation. Memory 340 may comprise any tangible, non-transitorycomputer-readable storage medium for storing data including electronic,magnetic, optical, electromagnetic, or semiconductor data storage.Memory 340 stores a computer program 350 comprising executableinstructions that configure the processing circuit 320 to implementmethods 400 according to FIG. 4 . In general, computer programinstructions and configuration information are stored in a non-volatilememory, such as a read only memory (ROM), erasable programmable readonly memory (EPROM) or flash memory. Temporary data generated duringoperation may be stored in a volatile memory, such as a random accessmemory (RAM). In some embodiments, the computer program 350 forconfiguring the processing circuit 320 as herein described may be storedin a removable memory, such as a portable compact disc, portable digitalvideo disc, or other removable media. The computer program 350 may alsobe embodied in a carrier such as an electronic signal, optical signal,radio signal, or computer readable storage medium.

FIG. 10 illustrates another embodiment of a wireless device 1000 inaccordance with various aspects as described herein. In some instances,the wireless device 1000 may be referred as a user equipment (UE), amobile station (MS), a terminal, a cellular phone, a cellular handset, apersonal digital assistant (PDA), a smartphone, a wireless phone, anorganizer, a handheld computer, a desktop computer, a laptop computer, atablet computer, a set-top box, a television, an appliance, a gamedevice, a medical device, a display device, a metering device, anInternet-of-Things (IoT) device, or some other like terminology.Further, the wireless device may operate over one or more frequencybands and one or more radio access technologies (RATs). In otherinstances, the wireless device 1000 may be a set of hardware components.

In FIG. 10 , the wireless device 1000 may be configured to include aprocessing circuit 1001 that is operatively coupled to an input/outputinterface 1005, a radio frequency (RF) interface 1009, a networkconnection interface 1011, a memory 1015 including a random accessmemory (RAM) 1017, a read only memory (ROM) 1019, a storage medium 1021or the like, a communication subsystem 1031, a power source 1033,another component, or any combination thereof. The storage medium 1021may include an operating system 1023, an application program 1025, data1027, or the like. Specific devices may utilize all of the componentsshown in FIG. 10 , or only a subset of the components, and levels ofintegration may vary from device to device. Further, specific devicesmay contain multiple instances of a component, such as multipleprocessing circuits, memories, transceivers, transmitters, receivers,etc. For instance, a computing device may be configured to include aprocessing circuit and a memory.

In FIG. 10 , the processing circuit 1001 may be configured to processcomputer instructions and data. The processing circuit 1001 may beconfigured as any sequential state machine operative to execute machineinstructions stored as machine-readable computer programs in the memory,such as one or more hardware-implemented state machines (e.g.,indiscrete logic, FPGA, ASIC, etc.); programmable logic together withappropriate firmware; one or more stored-program, general-purposeprocessing circuits, such as a microprocessor or Digital SignalProcessor (DSP), together with appropriate software; or any combinationof the above. For example, the processing circuit 1001 may include twocomputer processing circuits. In one definition, data is information ina form suitable for use by a computer. It is important to note that aperson having ordinary skill in the art will recognize that the subjectmatter of this disclosure may be implemented using various operatingsystems or combinations of operating systems.

In the current embodiment, the input/output interface 1005 may beconfigured to provide a communication interface to an input device,output device, or input and output device. The wireless device 1000 maybe configured to use an output device via the input/output interface1005. A person of ordinary skill will recognize that an output devicemay use the same type of interface port as an input device. For example,a USB port may be used to provide input to and output from the wirelessdevice 1000. The output device may be a speaker, a sound card, a videocard, a display, a monitor, a printer, an actuator, an emitter, asmartcard, another output device, or any combination thereof. Thewireless device 1000 may be configured to use an input device via theinput/output interface 1005 to allow a user to capture information intothe wireless device 1000. The input device may include a mouse, atrackball, a directional pad, a trackpad, a presence-sensitive inputdevice, a display such as a presence-sensitive display, a scroll wheel,a digital camera, a digital video camera, a web camera, a microphone, asensor, a smartcard, and the like. The presence-sensitive input devicemay include a digital camera, a digital video camera, a web camera, amicrophone, a sensor, or the like to sense input from a user. Thepresence-sensitive input device may be combined with the display to forma presence-sensitive display. Further, the presence-sensitive inputdevice may be coupled to the processing circuit. The sensor may be, forinstance, an accelerometer, a gyroscope, a tilt sensor, a force sensor,a magnetometer, an optical sensor, a proximity sensor, another likesensor, or any combination thereof. For example, the input device may bean accelerometer, a magnetometer, a digital camera, a microphone, and anoptical sensor.

In FIG. 10 , the RF interface 1009 may be configured to provide acommunication interface to RF components such as a transmitter, areceiver, and an antenna. The network connection interface 1011 may beconfigured to provide a communication interface to a network 1043 a. Thenetwork 1043 a may encompass wired and wireless communication networkssuch as a local-area network (LAN), a wide-area network (WAN), acomputer network, a wireless network, a telecommunications network,another like network or any combination thereof. For example, thenetwork 1043 a may be a Wi-Fi network. The network connection interface1011 may be configured to include a receiver and a transmitter interfaceused to communicate with one or more other nodes over a communicationnetwork according to one or more communication protocols known in theart or that may be developed, such as Ethernet, TCP/IP, SONET, ATM, orthe like. The network connection interface 1011 may implement receiverand transmitter functionality appropriate to the communication networklinks (e.g., optical, electrical, and the like). The transmitter andreceiver functions may share circuit components, software or firmware,or alternatively may be implemented separately.

In this embodiment, the RAM 1017 may be configured to interface via thebus 1002 to the processing circuit 1001 to provide storage or caching ofdata or computer instructions during the execution of software programssuch as the operating system, application programs, and device drivers.In one example, the wireless device 1000 may include at least onehundred and twenty-eight megabytes (128 Mbytes) of RAM. The ROM 1019 maybe configured to provide computer instructions or data to the processingcircuit 1001. For example, the ROM 1019 may be configured to beinvariant low-level system code or data for basic system functions suchas basic input and output (I/O), startup, or reception of keystrokesfrom a keyboard that are stored in a non-volatile memory. The storagemedium 1021 may be configured to include memory such as RAM, ROM,programmable read-only memory (PROM), erasable programmable read-onlymemory (EPROM), electrically erasable programmable read-only memory(EEPROM), magnetic disks, optical disks, floppy disks, hard disks,removable cartridges, flash drives. In one example, the storage medium1021 may be configured to include an operating system 1023, anapplication program 1025 such as a web browser application, a widget orgadget engine or another application, and a data file 1027.

In FIG. 10 , the processing circuit 1001 may be configured tocommunicate with a network 1043 b using the communication subsystem1031. The network 1043 a and the network 1043 b may be the same networkor networks or different network or networks. The communicationsubsystem 1031 may be configured to include one or more transceiversused to communicate with the network 1043 b. For example, thecommunication subsystem 1031 may be configured to include one or moretransceivers used to communicate with one or more remote transceivers ofanother wireless device such as a base station of a radio access network(RAN) according to one or more communication protocols known in the artor that may be developed, such as IEEE 802.xx, CDMA, WCDMA, GSM, LTE,UTRAN, WiMax, 5G NR, NB IoT, or the like.

In another example, the communication subsystem 1031 may be configuredto include one or more transceivers used to communicate with one or moreremote transceivers of another wireless device such as user equipmentaccording to one or more communication protocols known in the art orthat may be developed, such as IEEE 802.xx, CDMA, WCDMA, GSM, LTE,UTRAN, WiMax, 5G NR, NB IoT, or the like. Each transceiver may include atransmitter 1033 or a receiver 1035 to implement transmitter or receiverfunctionality, respectively, appropriate to the RAN links (e.g.,frequency allocations and the like). Further, the transmitter 1033 andthe receiver 1035 of each transceiver may share circuit components,software or firmware, or alternatively may be implemented separately. Inthe current embodiment, the communication functions of the communicationsubsystem 1031 may include data communication, voice communication,multimedia communication, short-range communications such as Bluetooth,near-field communication, location-based communication such as the useof the global positioning system (GPS) to determine a location, anotherlike communication function, or any combination thereof. For example,the communication subsystem 1031 may include cellular communication,Wi-Fi communication, Bluetooth communication, and GPS communication. Thenetwork 1043 b may encompass wired and wireless communication networkssuch as a local-area network (LAN), a wide-area network (WAN), acomputer network, a wireless network, a telecommunications network,another like network or any combination thereof. For example, thenetwork 1043 b may be a cellular network, a Wi-Fi network, and anear-field network. The power source 1013 may be configured to providean alternating current (AC) or direct current (DC) power to componentsof the wireless device 1000.

In FIG. 10 , the storage medium 1021 may be configured to include anumber of physical drive units, such as a redundant array of independentdisks (RAID), a floppy disk drive, a flash memory, a USB flash drive, anexternal hard disk drive, thumb drive, pen drive, key drive, ahigh-density digital versatile disc (HD-DVD) optical disc drive, aninternal hard disk drive, a Blu-Ray optical disc drive, a holographicdigital data storage (HDDS) optical disc drive, an external mini-dualin-line memory module (DIMM) synchronous dynamic random access memory(SDRAM), an external micro-DIMM SDRAM, a smartcard memory such as asubscriber identity module or a removable user identity (SIM/RUIM)module, other memory, or any combination thereof. The storage medium1021 may allow the wireless device 1000 to access computer executableinstructions, application programs or the like, stored on transitory ornon-transitory memory media, to off-load data, or to upload data. Anarticle of manufacture, such as one utilizing a communication system maybe tangibly embodied in storage medium 1021, which may comprise acomputer-readable medium.

The functionality of the methods described herein may be implemented inone of the components of the wireless device 1000 or partitioned acrossmultiple components of the wireless device 1000. Further, thefunctionality of the methods described herein may be implemented in anycombination of hardware, software or firmware. In one example, thecommunication subsystem 1031 may be configured to include any of thecomponents described herein. Further, the processing circuit 1001 may beconfigured to communicate with any of such components over the bus 1002.In another example, any of such components may be represented by programinstructions stored in memory that when executed by the processingcircuit 1001 performs the corresponding functions described herein. Inanother example, the functionality of any of such components may bepartitioned between the processing circuit 1001 and the communicationsubsystem 1031. In another example, the non-computative-intensivefunctions of any of such components may be implemented in software orfirmware and the computative-intensive functions may be implemented inhardware.

Furthermore, the various aspects described herein may be implementedusing standard programming or engineering techniques to producesoftware, firmware, hardware (e.g., circuits), or any combinationthereof to control a computing device to implement the disclosed subjectmatter. It will be appreciated that some embodiments may be comprised ofone or more generic or specialized processors such as microprocessors,digital signal processors, customized processors and field programmablegate arrays (FPGAs) and unique stored program instructions (includingboth software and firmware) that control the one or more processors toimplement, in conjunction with certain non-processor circuits, some,most, or all of the functions of the methods, devices and systemsdescribed herein. Alternatively, some or all functions could beimplemented by a state machine that has no stored program instructions,or in one or more application specific integrated circuits (ASICs), inwhich each function or some combinations of certain of the functions areimplemented as custom logic circuits. Of course, a combination of thetwo approaches may be used. Further, it is expected that one of ordinaryskill, notwithstanding possibly significant effort and many designchoices motivated by, for example, available time, current technology,and economic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The term “article of manufacture” as used herein is intended toencompass a computer program accessible from any computing device,carrier, or media. For example, a computer-readable medium may include:a magnetic storage device such as a hard disk, a floppy disk or amagnetic strip; an optical disk such as a compact disk (CD) or digitalversatile disk (DVD); a smart card; and a flash memory device such as acard, stick or key drive. Additionally, it should be appreciated that acarrier wave may be employed to carry computer-readable electronic dataincluding those used in transmitting and receiving electronic data suchas electronic mail (email) or in accessing a computer network such asthe Internet or a local area network (LAN). Of course, a person ofordinary skill in the art will recognize many modifications may be madeto this configuration without departing from the scope or spirit of thesubject matter of this disclosure.

Throughout the specification and the embodiments, the following termstake at least the meanings explicitly associated herein, unless thecontext clearly dictates otherwise. Relational terms such as “first” and“second,” and the like may be used solely to distinguish one entity oraction from another entity or action without necessarily requiring orimplying any actual such relationship or order between such entities oractions. The term “or” is intended to mean an inclusive “or” unlessspecified otherwise or clear from the context to be directed to anexclusive form. Further, the terms “a,” “an,” and “the” are intended tomean one or more unless specified otherwise or clear from the context tobe directed to a singular form. The term “include” and its various formsare intended to mean including but not limited to. References to “oneembodiment,” “a further embodiment,” “an embodiment,” “exampleembodiment,” “various embodiments,” and other like terms indicate thatthe embodiments of the disclosed technology so described may include aparticular function, feature, structure, or characteristic, but notevery embodiment necessarily includes the particular function, feature,structure, or characteristic. Further, repeated use of the phrase “inone embodiment” does not necessarily refer to the same embodiment,although it may.

1. A method, performed by a source base station, the method comprising:determining that a wireless device is to be handed over from the sourcebase station to a target base station; sending, to the target basestation in a handover signaling message, a current mapping between twoor more flow identifiers and a first data radio bearer used forcommunication between the wireless device and the source base station;receiving, from the target base station, an indication that the currentmapping is to be used; and handing over the wireless device from thesource base station to the target base station.
 2. The method of claim1, wherein the two or more flow identifiers are associated withrespective packet flows originating or terminating at the wirelessdevice.
 3. A source base station comprising: processing circuitry andmemory, the memory storing instructions executable by the processingcircuitry whereby the source base station is configured to: determinethat a wireless device is to be handed over from the source base stationto a target base station; send, in a handover signaling message to thetarget base station, a current mapping between two or more flowidentifiers and a first data radio bearer used for communication betweenthe wireless device and the source base station; receive, from thetarget base station, an indication that the current mapping should beused; and hand over the wireless device from the source base station tothe target base station.
 4. A method, performed by a target basestation, the method comprising: obtaining, from a handover signalingmessage received from a source base station, a current mapping betweentwo or more flow identifiers and a first data radio bearer used forcommunication between a wireless device and the source base station;determining a new mapping between the two or more flow identifiers and asecond data radio bearer used for communication between the wirelessdevice and the target base station, wherein the new mapping is the samemapping as the current mapping; indicating, to the source base station,that the current mapping is to be used for further communication withthe wireless device; accepting hand over of the wireless device from thesource base station to the target base station.
 5. The method of claim4, wherein obtaining the current mapping from the source base stationcomprises receiving the current mapping from the wireless device via thesource base station.
 6. The method of claim 4, wherein determining thenew mapping between the two or more flow identifiers and the second dataradio bearer comprises determining, after the wireless device has beenhanded over to the target base station, the new mapping as being betweenthe two or more flow identifiers and a new data radio bearer.
 7. Themethod of claim 4, wherein determining the new mapping comprisesdetermining the new mapping after the wireless device has been handedover to the target base station, the new mapping comprising a mappingbetween the two or more flow identifiers associated with one or moredownlink packet flows on a new data radio bearer used for communicationbetween the wireless device and the target base station.
 8. The methodof claim 7, further comprising transmitting, to the wireless device, theone or more downlink packet flows on the new data radio bearer based onthe new mapping and, in response, receiving, from the wireless device,one or more uplink packet flows on the new data radio bearer that aremapped to the two or more flow identifiers.
 9. The method of claim 4,wherein the two or more flow identifiers are associated with respectivepacket flows originating or terminating at the wireless device.
 10. Atarget base station comprising: processing circuitry and memory, thememory storing instructions executable by the processing circuitrywhereby the target base station is configured to: obtain, from ahandover signaling message received from a source base station, acurrent mapping between two or more flow identifiers, associated withrespective packet flows originating or terminating at the wirelessdevice, and a first data radio bearer used for communication between thewireless device and the source base station; determine a new mappingbetween the two or more flow identifiers and a second data radio bearerused for communication between the wireless device and the target basestation, wherein the new mapping is the same mapping as the currentmapping; and indicate, to the source base station, that the currentmapping is to be used for further communication with the wirelessdevice; accept hand over of the wireless device from the source basestation to the target base station.
 11. The target base station of claim10, wherein to obtain the current mapping from the source base station,the target base station is configured to receive the current mappingfrom the wireless device via the source base station.
 12. The targetbase station of claim 10, wherein to determine the new mapping betweenthe two or more flow identifiers and the second data radio bearer, thetarget base station is configured to determine, after the wirelessdevice has been handed over to the target base station, the new mappingas being between the two or more flow identifiers and a new data radiobearer.
 13. The target base station of claim 10, wherein to determinethe new mapping the target base station is configured to determine thenew mapping after the wireless device has been handed over to the targetbase station, the new mapping comprising a mapping between the two ormore flow identifiers associated with one or more downlink packet flowson a new data radio bearer used for communication between the wirelessdevice and the target base station.
 14. The target base station of claim13, wherein the target base station is further configured to transmit,to the wireless device, the one or more downlink packet flows on the newdata radio bearer based on the new mapping and, in response, receive,from the wireless device, one or more uplink packet flows on the newdata radio bearer that are mapped to the two or more flow identifiers.15. The target base station of claim 10, wherein the two or more flowidentifiers are associated with respective packet flows originating orterminating at the wireless device.
 16. A non-transitory computerreadable medium storing a computer program product for controlling asource base station in a communication network, the computer programproduct comprising software instructions that, when run on the sourcebase station, cause the source base station to: determine that awireless device is to be handed over from the source base station to atarget base station; send, to the target base station in a handoversignaling message, a current mapping between two or more flowidentifiers and a first data radio bearer used for communication betweenthe wireless device and the source base station; receive, from thetarget base station, an indication that the current mapping is to beused; and hand over the wireless device from the source base station tothe target base station.
 17. A non-transitory computer readable mediumstoring a computer program product for controlling a target base stationin a communication network, the computer program product comprisingsoftware instructions that, when run on the target base station, causethe target base station to: obtain, from a handover signaling messagereceived from a source base station, a current mapping between two ormore flow identifiers and a first data radio bearer used forcommunication between a wireless device and the source base station;determine a new mapping between the two or more flow identifiers and asecond data radio bearer used for communication between the wirelessdevice and the target base station, wherein the new mapping is the samemapping as the current mapping; indicate, to the source base station,that the current mapping is to be used for further communication withthe wireless device; accept hand over of the wireless device from thesource base station to the target base station.